Acceleration
ACCELERATION:: The time rate of change in velocity. The SI unit is meters per second2. http://www.glenbrook.k12.il.us/gbssci/phys/class/1DKin/U1L1e.html Acceleration measures the rate that velocity changes, therefore when velocity is constant (if a car is going at a constant 60 mph) then there is no acceleration. UNIFORM ACCELERATION Uniform acceleration refers to acceleration that has the same quanitity over a period of time. Imagine a graph that shows TIME on the x-axis and VELOCITY on the y-axis. If the line on this graph is a postive linear line, then the acceleration (slope of the line) is UNIFORM. Equations for Uniform Acceleration The equation for the uniform acceleration of an object is... a= change in V/t = V2-V1/t V2= V1+ a X t d= V1 x t + 1/2a X t2 v22= V12+ 2 x a x d Where a= acceleration, V1= initial velocity in meters/ second, V2= final velocity in meters/ second, d= distance in meters and t= time in seconds. Uniform Acceleration Questions The velocity of an object is +47 meters per second at 3.0 seconds and is +65 meters per second at 12.0 seconds. Calculate the acceleration of the object. Solutions to Problems Freely Falling Objects Freely falling objects refers to the motion of an object falling from rest ner the surface of the Earth (ignore air resistance). When looking at this motion for a varity of objects, it is noted that the velocity of the object increases uniformly at a rate of 9.8 meters/ second2. This number represents ACCELERATION DUE TO GRAVITY http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L5b.html. It is an important constant that is used in many different aspects of physics. Problems Using ACCELERATION DUE TO GRAVITY b. A ball is dropped fromthe roof of a building. What is the velocty of the ball after 4 seconds? How far does the ball fall during this time? Solutions to Problems Postive and Negative Acceleration As it is possible to have postive acceleration, it is possible to have negative acceleration as well. We looked at a moving car that was speeding up at a constant acceleration, but what happens when a car slows down? Imagine the postive linear graph described earlier, now think of it with a negative slope. As time passes, the velocity of the car doesn't increase it decreases. This is an example of negative acceleration. How to Find the Sign of Acceleration Imagine that the moving object is moving on a coordinate plane (you know, a graph). In every case, the coordinate axis should be parallel to the surfce of whatever the object is moving on. When the object is moving in the direction of the positve axis (nomally to the right) then the acceleration of that object is positive. Therefore, if the object is moving in the direction of the negative axis (left) then the acceleration is negative. Problem c. If a car is driving at 30 mph and then 10 seconds later is driving at 15 mph, is the acceleration of the car positive or negative? Solutions to Problems =References= 1. http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/1DKin/U1L5b.html 2. http://www.glenbrook.k12.il.us/gbssci/phys/class/1DKin/U1L1e.html =Resources= 1. Regents Review Book: Physics The Physical Setting 2. Glencoe Physics: Principles and Problems